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Lanthanide( 111) Complexes with Cyclooctatetraene Dianion. Synthetic Chemistry, Characterization, and Physical Properties' K. 0. Hodgson,2 F. Mares, D. F. Starks, and A. Streitwieser, Jr.* Contribution from the Department of Chemistry, University of California, Berkeley, California 94720. Received August 29, 1972 Abstract: This paper reports two series of lanthanide 7r-carbocyclic complexes of formula K[Ln(CsHs),] and [Ln(c&b)Cl .2C4H80]2. Single crystal X-ray structures of the cerium member of both series have been previously determined. Analytical and spectral data strongly suggest that the other lanthanide complexes in each series are isostructural with the cerium complexes. Chemical and spectral data show that these lanthanide cyclooctatetraenyl metallocenes are highly ionic relative to the analogous actiniLe complexes. This trend undoubtedly results from the inability of the lanthanide 4f orbitals to contribute to covalent bonding ielative to the 5f orbitals. Similar properties are found for the corresponding complex with yttrium, a metal which is not a lanthanide rare earth. Using Raman techniques the symmetrical ring-metal stretch of eight-membered ring metallocenes was measured.
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nterest in the chemistry of organometallic compounds of the lanthanide transition metals has expanded rspidly within the past few years. This renaissance of interest is partly due to the preparation of uranocene," U(C8H&, and subsequent isostructural complexes of thorium4 and neptunium and p1utonium.j Preparation of the complex U(CsH& was of particular significance because its preparation derived from the expectation that covalent stabilization may result from overlap of 5f orbitals with a symmetry-allowed combination of the highest occupied orbitals in the cyclooctatetraene dianion ligands.6-* Additional evidence for this view is provided by nmrg and chemical6 studies. A complete development of this organometallic chemistry now requires extension of the synthetic chemistry of the 5f elements into the 4f or lanthanide series and a comparison of these chemical, physical, and structural characteristics of the two series. Until recently, little has been known about the structural chemistry of the 14 lanthanide elements which exist predominantly in the 3 f oxidation state. Much of the earlier work emphasized only synthesis and used primarily chemical analysis of the compounds and chemical analogy for structural postulates. The first 7r-carbocyclic complexes of the lanthanides were the triscyclopentadienyls Ln(CjH& (where Ln is any lanthanide ion) reported by Birmingham and Wilkinson in 1954. lo Subsequently, complexes of the type Ln(C5Hj)2C111and
Ln(CjHj)CI2l2were reported and characterized, as well as the preparation of the biscyclopentadienyl compounds of Eu" and Yb11.13 Recent reviews on these lanthanide organometallic compounds are available.14 In general, all of these lanthanide complexes exhibit similar chemical and physical properties. With the exception of the dimeric [Ln(CjH&. XI, compounds, where X = phenoxide or carboxylate,ll all of the complexes are hydrolytically and oxidatively unstable and show pronounced ligand lability. In essence, they behave as essentially ionic compounds. l 5 This predominantly ionic character suggests that the T complexes with C8Hs dianion would be important reference compounds for comparison with the related actinide complexes. The first such complexes of lanthanides with CsHs dianion, reported by Hayes and Thomas, l 6 were the 1 : 1 complexes vith the 2+ oxidation states of Eu and Yb. Preliminary reports have already appeared on our preparations of two series of C8H8-1anthanide complexes of general type [Ln(C8H8)2]K17 and [Ln(C8Hs)Cl* 2C4H80I2. I* In rhe present paper we give experimental details on the preparation of these difficult to handle compounds, we consider their characterization in detail and we report their physical properties, including Raman spectra. Finally, their electronic structure and bonding as related to the actinide complexes are discussed in light of the detailed molecular structure.
(1) This research was supported in part by National Science Foundation Grants 6125 and 13369. (2) National Science Foundation Trainee, 1969-1972. (3) A. Streitwieser, Jr., and U. Muller-Westerhoff, J. Amer. Chem. Soc., 90,7364 (1968). (4) A. Streitwieser, Jr., and N. Yoshida, J . Amer. Chem. Soc., 91, 7528 (1969). ( 5 ) D. G . Karraker, J. A. Stone, E. R . Jones, Jr., and N. Edelstein, J . Amer. Chem. Soc., 92,4841 (1970). (6) A. Streitwieser, Jr., U. Muller-Westerhoff, G. Sonnichsen, F. Mares, D. Morrell, K. 0. Hodgson, and C. Harmon, J . Amer. Chem. Soc., 95,8644 (1973). (7) R. G. Hayes and N. Edelstein, J. Amer. Chem. Soc., 94. 8688 (1972). (8) See also R . D. Fischer, Theor. Chim. Acta, 1,418 (1963). (9) (a) N. Edelstein, G. N. LaMar, F. Mares, and A. Streitwieser, Jr., Chem. PI2j.s. Lett., 8, 399 (1971); (b) A. Streitwieser, Jr., D. Uempf, G . N. LaMar, D. G. Karraker, and N. Edelstein, J . Amer. Chem. Soc., 93, 7343 (1971). (10) G. Wilkinson and J. M. Birmingham, J. Amer. Chem. Soc., 76, 6210 (1954); J. M. Birmingham and G. Wilkinson, J. Amer. Chem. Soc., 78, 42 (1956). (11) R . E. Maginn, S. Manastyrskyj, and M. Dubeck, J. Amer. Chem. Soc., 85, 672 (1963).
A description of the apparatus and techniques used in the synthesis and purification of the complexes can be found in the accompanying paper describing the detailed preparation of U(CSHS).Z.~
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Experimental Section
(12) S. Manastyrskyj, R. E. Maginn, and M. Dubeck, Inorg. Chem., 2, 904 (1963). (13) E. 0. Fischer and H. Fischer,J. Organometal. Chem., 3,181 (1965). (14) R. G . Hayes and J. L. Thomas, Organometal. Chem. Reu., 7 , 1 (1971); B. Kanellakopulos and K. W. Bagnall, in "International Review of Science, Inorganic Chemistry, Series 1, Vol. 7, Lanthanides and Actinides," K. W. Bagnall, Ed., Butterworths, London, 1972, p 299. (15) The electronic spectra of several Ln(CsH5)s compounds have been interpreted to indicate little covalency in iing-metal bonding: L. J. Nugent, P. G. Laubereau, G. K . Werner, and I
